1. Field of the Invention
The present invention generally relates to electronic components and more particularly, to a method of accommodating an electronic component in an outer casing, by which an element itself of the electronic component such as a piezoelectric resonator or the like subjected to mechanical vibration is sheathed or encapsulated in the hollow outer casing.
2. Description of the Prior Art
Conventionally, in methods of this kind, it has been so arranged that electronic components such as integrated circuits, etc. are sheathed, i.e., encapsulated, by transfer molding in which epoxy resin is charged into a mold. However, it has been difficult to sheathe or encapsulate, by the transfer molding, elements themselves of electronic components such as piezoelectric resonators, acoustic vibrators, etc. with sheathing casings in which space for allowing them to mechanically vibrate is required to be formed.
Thus, in order to sheathe or encapsulate the elements themselves of the electronic components of this kind, it has been conventionally so arranged that a pair of sheathing casings made of ceramic and having a hollow structure are bonded to each other by the use of low-melting glass, adhesive, etc. However, this prior art sheathing method has such inconveniences that it becomes difficult not only to apply low-melting glass, adhesive, etc. to mating surfaces of the sheathing casings, but to position the sheathing casings accurately when the sheathing casings become compact for sheathing electronic components small in size. Furthermore, the prior art sheathing method has such disadvantages as requirements for long curing time, high curing temperature, low production efficiency, etc.
Consequently, in order to eliminate the above described inconveniences of the prior art sheathing methods, an improved sheathing method was proposed in Japanese Patent Application No. 117315/1982 (Tokugansho 57-117315) filed on July 5, 1982, of which the present inventor is one of the co-inventors and which is assigned to the same assignee as the present case. In the proposed method, a terminal frame formed by a metallic plate having a shape of a frame for securing an electronic component thereto is interposed between a pair of sheathing casings made of thermoplastic resin. Each is formed with a recessed portion. The terminal frame is electrically heated, so that mating faces of the sheathing cases are attached to each other through melting thereof. More specifically, referring to FIGS. 1 to 3, in the proposed method, an acoustic vibrator 11 supported by a terminal frame 12 is accommodated in a pair of a first sheathing casing 13 and a second sheathing casing 14 attached to each other.
The acoustic vibrator 11 includes a square frame member 15 formed by blanking a metallic plate made of metals having a constant modulus of elasticity, such as elinvar, etc., a rectangular acoustic vibrator body 17 provided inside the frame member 15, and coupling pieces 16a, 16b, 16c and 16d for supporting, at node portions of vibration of the acoustic vibrator body 17, the acoustic vibrator body 17. The coupling pieces 16a and 16d and the coupling pieces 16b and 16c are, respectively, provided at opposite sides of the acoustic vibrator body 17 symmetrically. A piezoelectric film 18 made of piezoelectric materials such as zinc oxide, etc. is formed on upper faces of the acoustic vibrator body 17. The coupling piece 16a and one portion of the frame member 15 adjacent to the coupling piece 16a are shown in FIG. 1. It should be noted here that the hatching in FIG. 1 does not illustrate a cross-section of the acoustic vibrator 11, but is given only for depicting the piezoelectric film 18 for convenience. Furthermore, a drive electrode film 19a, a lead electrode film 19b and an outlet electrode film 19c are formed on the piezoelectric film 18. It is to be further noted that the piezoelectric film 18 disposed under the lead electrode film 19b and the outlet electrode film 19c functions as an insulating layer.
Meanwhile, the terminal frame 12 has a frame portion of substantially square annular shape and includes a pair of U-shaped projections 21a and 21d projecting outwardly from opposite ends of one side of the frame portion in parallel with each other, a pair of U-shaped projections 21b and 21c projecting outwardly from opposite ends of the other side of the frame portion in alignment with the projections 21a and 21d, respectively, supporting pieces 20a, 20b, 20c and 20d protruding inwardly from the terminal frame 12 and disposed adjacent to the projections 21a, 21b, 21c and 21d, respectively, and lead terminals 22a, 22b, 22c and 22d projecting outwardly from the projections 21a, 21b, 21c and 21d in the same directions as the projections 21a, 21b, 21c and 21d, respectively. The supporting pieces 20a and 20b are provided diagonally symmetrically with respect to the supporting pieces 20c and 20d, respectively. As shown in FIG. 2, the projections 21a, 21b, 21c and 21d have a pair of leg portions 21al and 21a2, a pair of leg portions 21bl and 21b2, a pair of leg portions 21cl and 21c2 and a pair of leg portions 21dl and 21d2, respectively.
The first sheathing casing 13 of FIG. 1 and the second sheathing casing 14 of FIG. 1 each are formed into a square plate by molding thermoplastic resin such as polycarbonate, polyacetal, polyethylene, etc. and have mating faces 13b and 14b formed at peripheral side edges thereof, respectively and square recessed portions 13a and 14a enclosed by the mating faces 13b and 14b, respectively, such that the acoustic vibrator 11 is accommodated in the recessed portions 13a and 14a, with the mating faces 13b and 14b confronting each other. It is to be noted here that the frame portion of the terminal frame 12 is arranged to correspond, in configuration, to the mating faces 13b and 14b.
As shown in FIG. 2, the terminal frame 12 having the acoustic vibrator 11 secured to the supporting pieces 20a to 20d by welding (not shown) or by the use of electrically conductive adhesive (not shown) is interposed between the first sheathing casing 13 and the second sheathing casing 14 such that the supporting piece 20a is connected to the outlet electrode film 19b by the use of solder, bonding agent or electrically conductive adhesive or through mere contact therebetween, with the terminal frame 12 being in contact with the mating faces 13b and 14b. Then, the terminal frame 12 is electrically conducted or subjected to induction heating so as to be heated. When the terminal frame 12 is heated, the mating faces 13b and 14b in contact with the terminal frame 12 melt. Thereafter, when heating of the terminal frame 12 is stopped so as to lower the temperature of the terminal frame 12, the first sheathing casing 13 and the second sheathing casing 14 are attached to each other by thermoplastic resin forming the first sheathing casing 13 and the second, sheathing casing 14, whereby the acoustic vibrator 11 of FIG. 1 is accommodated in the recessed portions 13a and 14a.
Subsequently, when, for example, the leg portion 21a2 disposed inwardly of the leg portion 21a2 of the projection 21a and the leg portion 21b2 disposed inwardly of the leg portion 21b1 of the projection 21b are cut off as shown in dotted lines in FIG. 2, the lead terminals 22a and 22b are electrically conducted to the drive electrode film 19a, and the lead terminals 22c and 22d are electrically conducted to the acoustic vibrator body 17.
When the projections 21a to 21d of the terminal frame 12 are bent at right angles to the frame portion of the terminal frame 12 towards the second sheathing casing 14 and then, the lead terminals 22a to 22d are cut to a proper length, an acoustic vibrating component having a dual in-line type terminal structure can be obtained.
Furthermore, when, for example, the projections 21b and 21c projecting from one side of the first sheathing casing 13 and the second sheathing casing 14 are cut off before the projections 21a to 21d are bent at right angles to the frame portion of the terminal frame 12 towards the second sheathing casing 14 as described above, an acoustic vibrating component having a single in-line terminal structure constituted by the lead terminals 22a and 22d projecting from the other side of the first sheathing casing 13 and the second sheathing casing 14 can be obtained.
Moreover, the terminal frame 12 can be replaced by a terminal frame 12' shown in FIG. 3. The terminal frame 12' includes supporting pieces 20c' and 20d' in place of the supporting pieces 20c and 20d of the terminal frame 12, respectively. Namely, the supporting piece 20c' projects inwardly from the terminal frame 12' in parallel with the supporting piece 20b, while the projecting piece 20d' projects inwardly from the terminal frame 12' so as to confront the supporting piece 20a.
However, the above described method proposed in the Japanese Patent Application No. 117315/1982 has such inconveniences that, since the lead terminals 22a to 22d of the terminal frame 12 are used as terminals for electrical conduction for heating the terminal frame 12, electric current is caused to flow through the lead terminals 22a to 22d when the terminal frame 12 is electrically conducted so as to be heated, with the result that solder deposited on the lead terminals 22a to 22d are removed therefrom, etc.